# Logs Data Model **Status**: [Stable](../document-status.md)

Table of Contents

- [Design Notes](#design-notes) * [Requirements](#requirements) * [Events](#events) * [Field Kinds](#field-kinds) - [Log and Event Record Definition](#log-and-event-record-definition) * [Field: `Timestamp`](#field-timestamp) * [Field: `ObservedTimestamp`](#field-observedtimestamp) * [Trace Context Fields](#trace-context-fields) + [Field: `TraceId`](#field-traceid) + [Field: `SpanId`](#field-spanid) + [Field: `TraceFlags`](#field-traceflags) * [Severity Fields](#severity-fields) + [Field: `SeverityText`](#field-severitytext) + [Field: `SeverityNumber`](#field-severitynumber) + [Mapping of `SeverityNumber`](#mapping-of-severitynumber) + [Reverse Mapping](#reverse-mapping) + [Error Semantics](#error-semantics) + [Displaying Severity](#displaying-severity) + [Comparing Severity](#comparing-severity) * [Field: `Body`](#field-body) * [Field: `Resource`](#field-resource) * [Field: `InstrumentationScope`](#field-instrumentationscope) * [Field: `Attributes`](#field-attributes) + [Errors and Exceptions](#errors-and-exceptions) * [Field: `EventName`](#field-eventname) - [Example Log Records](#example-log-records) - [Example Mappings](#example-mappings) - [References](#references)

This is a data model and semantic conventions that allow to represent logs from various sources: application log files, machine generated events, system logs, etc. Existing log formats can be unambiguously mapped to this data model. Reverse mapping from this data model is also possible to the extent that the target log format has equivalent capabilities. The purpose of the data model is to have a common understanding of what a log record is, what data needs to be recorded, transferred, stored and interpreted by a logging system. This proposal defines a data model for [Standalone Logs](../glossary.md#standalone-log). ## Design Notes ### Requirements The Data Model was designed to satisfy the following requirements: - It should be possible to unambiguously map existing log formats to this Data Model. Translating log data from an arbitrary log format to this Data Model and back should ideally result in identical data. - Mappings of other log formats to this Data Model should be semantically meaningful. The Data Model must preserve the semantics of particular elements of existing log formats. - Translating log data from an arbitrary log format A to this Data Model and then translating from the Data Model to another log format B ideally must result in a meaningful translation of log data that is no worse than a reasonable direct translation from log format A to log format B. - It should be possible to efficiently represent the Data Model in concrete implementations that require the data to be stored or transmitted. We primarily care about 2 aspects of efficiency: CPU usage for serialization/deserialization and space requirements in serialized form. This is an indirect requirement that is affected by the specific representation of the Data Model rather than the Data Model itself, but is still useful to keep in mind. The Data Model aims to successfully represent 3 sorts of logs and events: - System Formats. These are logs and events generated by the operating system and over which we have no control - we cannot change the format or affect what information is included (unless the data is generated by an application which we can modify). An example of system format is Syslog. - Third-party Applications. These are generated by third-party applications. We may have certain control over what information is included, e.g. customize the format. An example is Apache log file. - First-party Applications. These are applications that we develop and we have some control over how the logs and events are generated and what information we include in the logs. We can likely modify the source code of the application if needed. ### Events Events are OpenTelemetry's standardized format for LogRecords. All semantic conventions defined for logs SHOULD be formatted as Events. Requirements and details for the Event format can be found in the [semantic conventions](https://github.com/open-telemetry/semantic-conventions/blob/main/docs/general/events.md). Events are intended to be used by OpenTelemetry instrumentation. It is not a requirement that all LogRecords are formatted as Events. ### Field Kinds This Data Model defines a logical model for a log record (irrespective of the physical format and encoding of the record). Each record contains 2 kinds of fields: - Named top-level fields of specific type and meaning. - Fields stored as [Attribute Collections](../common/README.md#attribute-collections), whose values are [AnyValue](../common/README.md#anyvalue). The keys and values for well-known fields follow semantic conventions for key names and possible values that allow all parties that work with the field to have the same interpretation of the data. See references to semantic conventions for `Resource` and `Attributes` fields and examples in [Appendix A](./data-model-appendix.md#appendix-a-example-mappings). The reasons for having these 2 kinds of fields are: - Ability to efficiently represent named top-level fields, which are almost always present (e.g. when using encodings like Protocol Buffers where fields are enumerated but not named on the wire). - Ability to enforce types of named fields, which is very useful for compiled languages with type checks. - Flexibility to represent less frequent data in Attribute Collections. This includes well-known data that has standardized semantics as well as arbitrary custom data that the application may want to include in the logs. When designing this data model we followed the following reasoning to make a decision about when to use a top-level named field: - The field needs to be either mandatory for all records or be frequently present in well-known log and event formats (such as `Timestamp`) or is expected to be often present in log records in upcoming logging systems (such as `TraceId`). - The field’s semantics must be the same for all known log and event formats and can be mapped directly and unambiguously to this data model. Both of the above conditions were required to give the field a place in the top-level structure of the record. ## Log and Event Record Definition [Appendix A](./data-model-appendix.md#appendix-a-example-mappings) contains many examples that show how existing log formats map to the fields defined below. If there are questions about the meaning of the field reviewing the examples may be helpful. Here is the list of fields in a log record: | Field Name | Description | | ---------- | ----------- | | Timestamp | Time when the event occurred. | | ObservedTimestamp | Time when the event was observed. | | TraceId | Request trace id. | | SpanId | Request span id. | | TraceFlags | W3C trace flag. | | SeverityText | The severity text (also known as log level). | | SeverityNumber | Numerical value of the severity. | | Body | The body of the log record. | | Resource | Describes the source of the log. | | InstrumentationScope | Describes the scope that emitted the log. | | Attributes | Additional information about the event. | | EventName | Name that identifies the class / type of event. | Below is the detailed description of each field. ### Field: `Timestamp` Type: Timestamp, uint64 nanoseconds since Unix epoch. Description: Time when the event occurred measured by the origin clock, i.e. the time at the source. This field is optional, it may be missing if the source timestamp is unknown. ### Field: `ObservedTimestamp` Type: Timestamp, uint64 nanoseconds since Unix epoch. Description: Time when the event was observed by the collection system. For events that originate in OpenTelemetry (e.g. using OpenTelemetry Logging SDK) this timestamp is typically set at the generation time and is equal to Timestamp. For events originating externally and collected by OpenTelemetry (e.g. using Collector) this is the time when OpenTelemetry's code observed the event measured by the clock of the OpenTelemetry code. This field SHOULD be set once the event is observed by OpenTelemetry. For converting OpenTelemetry log data to formats that support only one timestamp or when receiving OpenTelemetry log data by recipients that support only one timestamp internally the following logic is recommended: - Use `Timestamp` if it is present, otherwise use `ObservedTimestamp`. ### Trace Context Fields #### Field: `TraceId` Type: byte sequence. Description: Request trace id as defined in [W3C Trace Context](https://www.w3.org/TR/trace-context/#trace-id). Can be set for logs that are part of request processing and have an assigned trace id. This field is optional. #### Field: `SpanId` Type: byte sequence. Description: Span id. Can be set for logs that are part of a particular processing span. If SpanId is present TraceId SHOULD be also present. This field is optional. #### Field: `TraceFlags` Type: byte. Description: Trace flag as defined in [W3C Trace Context](https://www.w3.org/TR/trace-context/#trace-flags) specification. At the time of writing the specification defines one flag - the SAMPLED flag. This field is optional. ### Severity Fields #### Field: `SeverityText` Type: string. Description: severity text (also known as log level). This is the original string representation of the severity as it is known at the source. If this field is missing and `SeverityNumber` is present then the short name that corresponds to the `SeverityNumber` may be used as a substitution. This field is optional. #### Field: `SeverityNumber` Type: number. Description: numerical value of the severity, normalized to values described in this document. This field is optional. `SeverityNumber` is an integer number. Smaller numerical values correspond to less severe events (such as debug events), larger numerical values correspond to more severe events (such as errors and critical events). For example `SeverityNumber=17` describes an error that is less critical than an error with `SeverityNumber=20`. The following table defines the meaning of `SeverityNumber` value: | SeverityNumber range | Range name | Meaning | | -------------------- | ---------- | --------------------------------------------------------------------------------------- | | 1-4 | TRACE | A fine-grained debugging event. Typically disabled in default configurations. | | 5-8 | DEBUG | A debugging event. | | 9-12 | INFO | An informational event. Indicates that an event happened. | | 13-16 | WARN | A warning event. Not an error but is likely more important than an informational event. | | 17-20 | ERROR | An error event. Something went wrong. | | 21-24 | FATAL | A fatal error such as application or system crash. | `SeverityNumber=0` MAY be used to represent an unspecified value. #### Mapping of `SeverityNumber` Mappings from existing logging systems and formats (or **source format** for short) must define how severity (or log level) of that particular format corresponds to `SeverityNumber` of this data model based on the meaning given for each range in the above table. If the source format has more than one severity that matches a single range in this table then the severities of the source format must be assigned numerical values from that range according to how severe (important) the source severity is. For example if the source format defines "Error" and "Critical" as error events and "Critical" is a more important and more severe situation then we can choose the following `SeverityNumber` values for the mapping: "Error"->17, "Critical"->18. If the source format has only a single severity that matches the meaning of the range then it is recommended to assign that severity the smallest value of the range. For example if the source format has an "Informational" log level and no other log levels with similar meaning then it is recommended to use `SeverityNumber=9` for "Informational". Source formats that do not define a concept of severity or log level MAY omit `SeverityNumber` and `SeverityText` fields. Backend and UI may represent log records with missing severity information distinctly or may interpret log records with missing `SeverityNumber` and `SeverityText` fields as if the `SeverityNumber` was set equal to INFO (numeric value of 9). #### Reverse Mapping When performing a reverse mapping from `SeverityNumber` to a specific format and the `SeverityNumber` has no corresponding mapping entry for that format then it is recommended to choose the target severity that is in the same severity range and is closest numerically. For example Zap has only one severity in the INFO range, called "Info". When doing reverse mapping all `SeverityNumber` values in INFO range (numeric 9-12) will be mapped to Zap’s "Info" level. #### Error Semantics If `SeverityNumber` is present and has a value of ERROR (numeric 17) or higher then it is an indication that the log record represents an erroneous situation. It is up to the reader of this value to make a decision on how to use this fact (e.g. UIs may display such errors in a different color or have a feature to find all erroneous log records). If the log record represents an erroneous event and the source format does not define a severity or log level concept then it is recommended to set `SeverityNumber` to ERROR (numeric 17) during the mapping process. If the log record represents a non-erroneous event the `SeverityNumber` field may be omitted or may be set to any numeric value less than ERROR (numeric 17). The recommended value in this case is INFO (numeric 9). See [Appendix B](./data-model-appendix.md#appendix-b-severitynumber-example-mappings) for more mapping examples. #### Displaying Severity The following table defines the recommended short name for each `SeverityNumber` value. The short name can be used for example for representing the `SeverityNumber` in the UI: | SeverityNumber | Short Name | | -------------- | ---------- | | 1 | TRACE | | 2 | TRACE2 | | 3 | TRACE3 | | 4 | TRACE4 | | 5 | DEBUG | | 6 | DEBUG2 | | 7 | DEBUG3 | | 8 | DEBUG4 | | 9 | INFO | | 10 | INFO2 | | 11 | INFO3 | | 12 | INFO4 | | 13 | WARN | | 14 | WARN2 | | 15 | WARN3 | | 16 | WARN4 | | 17 | ERROR | | 18 | ERROR2 | | 19 | ERROR3 | | 20 | ERROR4 | | 21 | FATAL | | 22 | FATAL2 | | 23 | FATAL3 | | 24 | FATAL4 | When an individual log record is displayed it is recommended to show both `SeverityText` and `SeverityNumber` values. A recommended combined string in this case begins with the short name followed by `SeverityText` in parenthesis. For example "Informational" Syslog record will be displayed as **INFO (Informational)**. When for a particular log record the `SeverityNumber` is defined but the `SeverityText` is missing it is recommended to only show the short name, e.g. **INFO**. When drop down lists (or other UI elements that are intended to represent the possible set of values) are used for representing the severity it is preferable to display the short name in such UI elements. For example a dropdown list of severities that allows filtering log records by severities is likely to be more usable if it contains the short names of `SeverityNumber` (and thus has a limited upper bound of elements) compared to a dropdown list, which lists all distinct `SeverityText` values that are known to the system (which can be a large number of elements, often differing only in capitalization or abbreviated, e.g. "Info" vs "Information"). #### Comparing Severity In the contexts where severity participates in less-than / greater-than comparisons `SeverityNumber` field should be used. Special handling MAY be given to `SeverityNumber=0` when it is used to represent an unspecified severity. ### Field: `Body` Type: [AnyValue](../common/README.md#anyvalue). Description: A value containing the body of the log record. Can be for example a human-readable string message (including multi-line) describing the event in a free form or it can be a structured data composed of arrays and maps of other values. Body MUST support [AnyValue](../common/README.md#anyvalue) to preserve the semantics of structured logs emitted by the applications. Can vary for each occurrence of the event coming from the same source. This field is optional. ### Field: `Resource` Type: [Resource](../resource/sdk.md). Description: Describes the source of the log, aka [resource](../overview.md#resources). Multiple occurrences of events coming from the same event source can happen across time and they all have the same value of `Resource`. Can contain for example information about the application that emits the record or about the infrastructure where the application runs. Data formats that represent this data model may be designed in a manner that allows the `Resource` field to be recorded only once per batch of log records that come from the same source. SHOULD follow OpenTelemetry [semantic conventions for Resources](https://github.com/open-telemetry/semantic-conventions/blob/main/docs/resource/README.md). This field is optional. ### Field: `InstrumentationScope` Type: [Instrumentation Scope](../common/instrumentation-scope.md). Description: the [instrumentation scope](../common/instrumentation-scope.md). Multiple occurrences of events coming from the same scope can happen across time and they all have the same value of `InstrumentationScope`. This field is optional. ### Field: `Attributes` Type: [Attribute Collection](../common/README.md#attribute-collections). Description: Additional information about the specific event occurrence. Unlike the `Resource` field, which is fixed for a particular source, `Attributes` can vary for each occurrence of the event coming from the same source. Can contain information about the request context (other than [Trace Context Fields](#trace-context-fields)). This field is optional. #### Errors and Exceptions Additional information about errors and/or exceptions that are associated with a log record MAY be included in the structured data in the `Attributes` section of the record. If included, they MUST follow the OpenTelemetry [semantic conventions for exception-related attributes](https://github.com/open-telemetry/semantic-conventions/blob/main/docs/exceptions/exceptions-logs.md). ### Field: `EventName` Type: string. Description: Name that identifies the class / type of the [Event](#events). This name SHOULD uniquely identify the event structure (both attributes and body). A log record with a non-empty event name is an [Event](#events). ## Example Log Records For example log records see [JSON File serialization](../protocol/file-exporter.md#examples). ## Example Mappings For example log format mappings, see the [Data Model Appendix](./data-model-appendix.md). ## References - Log Data Model [OTEP 0097](../../oteps/logs/0097-log-data-model.md) - [Draft discussion of Data Model](https://docs.google.com/document/d/1ix9_4TQO3o-qyeyNhcOmqAc1MTyr-wnXxxsdWgCMn9c/edit#) - [Discussion of Severity field](https://docs.google.com/document/d/1WQDz1jF0yKBXe3OibXWfy3g6lor9SvjZ4xT-8uuDCiA/edit#)